1. Field of the Invention
The present invention relates to the field of a semiconductor processing and more specifically to a method and apparatus for controlling the crystal structure of a silicon film.
2. Discussion of Related Art
In order to fabricate more complex and higher density integrated circuits such as microprocessors and memories, device features must be continually reduced. An important feature which must be reduced in order to increase device density is the polysilicon gate lengths and correspondingly the polysilicon thickness of MOS transistors. Present polysilicon deposition processes form polysilicon films 602 having large and columnar grains 604 as shown in FIG. 6. As transistor gate lengths are shrunk to less than 0.18 microns the large and columnar grains 604 are beginning to play a critical role in the performance of the transistor. Dopants 606 which are subsequently added to the polysilicon film in order to reduce the resistance of the film utilize the grain boundaries 608 to diffuse throughout the polysilicon film 602. Because in prior art processes the grains 604 are large and columnar dopant diffusion is restricted causing areas 610 of undoped polysilicon, especially at the polysilicon 602/gate dielectric 612 interface. The lack of uniform distribution of dopants, known as poly depletion effects, detrimentally affects the performance of the fabricated transistor especially as a gate lengths decrease to below 0.18 microns.
Thus, what it desired a method of forming a polysilicon film with small and random grains so that narrow width gate length electrodes can be fabricated without suffering from poly depletion effects.
A method and apparatus for forming a polycrystalline silicon film. According to the present invention a process gas mix comprising a silicon source gas and a dilution gas mix is fed into a chamber wherein the dilution gas mix comprises H2 and an inert gas. A polycrystalline silicon film is then formed from the process gas mix.